The present invention relates to a water-cooled or air-cooled type heat source apparatus having a refrigerating cycle, in which an electronic expansion valve automatically adjusts an amount of a refrigerant flowing into an evaporator according to an operating state, and a method of starting the apparatus.
In a refrigerating apparatus which is a heat source apparatus, a compressor, a condenser, an electronic expansion valve, and an evaporator are provided.
A temperature detector detects super-heat of a refrigerant sucked into the compressor and an opening degree of the electronic expansion valve is controlled so that the detected super-heat falls in a predetermined range.
Hereupon, super-heat of a refrigerant sucked into the compressor assumes a relatively small value in the order of 3 to 5 K. Therefore, taking account of a detection error in the temperature detector, control of an opening degree of the electronic expansion valve involves a large error due to a detected temperature of the temperature detector, so that the compressor may be damaged due to liquid back.
Hereupon, JP-A-2003-106610 describes a technology, in which attention is paid to the fact that a super-heat of a refrigerant discharged from a compressor assumes a relatively large value of around 25 K and an opening degree of an electronic expansion valve is controlled in view of not only a suction super-heat but also a discharge super-heat.
That is, there is disclosed a technology of judging whether a suction super-heat as detected is larger or smaller than an actual super-heat, from a discharge super-heat, and changing a control target value of suction super-heat to control.
By the way, a screw chiller unit employing a conventional electronic expansion valve adopts control, in which after the electronic expansion valve is opened at a predetermined opening degree at the time of starting, an opening degree of the electronic expansion valve is decreased according to super-heat of refrigerant at a suction side of the compressor.
In this case, a speed, at which an opening degree of the electronic expansion valve is decreased, is difficult to control since it is necessary to avoid freezing of water or brine in an evaporator, which is caused when pressure and temperature of a refrigerant rapidly decrease.
Consequently, it takes time in closing the electronic expansion valve until a unit operates stably.
Accordingly, it is feared that an operation is prolonged in a state, in which liquid back to a screw compressor is apt to occur, to cause shortage of an oil film on a rotor part in the screw compressor, and there is a possibility that damage is given to a screw rotor.
Hereupon, while it is conceivable to use the technology described in JP-A-2003-106610 to control an opening degree of an electronic expansion valve, correction of a detection error of a suction side super-heat can be achieved but it is difficult to realize shortening of an operating time from starting till a stable operation.
Further, when a pseudo azeotropic refrigerant such as R410A, R134A, R404A, R32, R22, etc. or a single refrigerant is used as a refrigerant, temperature gradient is absent in a gas-liquid saturation region. Therefore, since temperature is constant at a certain pressure, at what refrigerant dryness a refrigerant is sucked into a compressor is not understandable in a state, in which a compressor suction side refrigerant super-heat is negative (compressor suction gas temperature<saturation temperature at compressor suction pressure), that is, a state of liquid back, so that there is a fear that control becomes difficult such as rapidly excessive throttling of an opening degree of an expansion valve.